THE PATENTS ACT 1970 [39 OF 1970]
THE PATENTS (AMENDMENT) RULES, 2006 COMPLETE SPECIFICATION
[See Section 10; rule 13]
"DISC MAGNET MOTORS WITH SPECIAL POLE SHAPE"
PORTESCAP INDIA PVT LTD, an Indian Company, of Unit No. 2, SDF 1, Seepz-SEZ, Andheri East Mumbai 400096, India,
The following specification particularly describes the invention and the manner in
which It Is to be performed.

[0001] The present disclosure relates to electrical machines, such as, axial flux disc magnet motors, using a stator assembly incorporated with special pole shape design to reduce generation of detent torque and provide a constant torque output.
[0002] Axial flux disc magnet motors provide low inertia and high acceleration. Thus, for example this motor is used in textile machinery for driving yarn guides.
[0003] In the existing designs, a rotor includes a disc magnet, a stator includes of plurality of elemental magnetic circuits using laminations having "C" shape. The lamination stacks having "C" shape are located in front of the disc magnet. The motor being a brushless type with an iron core stator structure presents detent torque. Each lamination stack creates its own detent torque and is used to guide magnetic flux with a direct impact on motor torque constant in amplitude and in shape.
[0004] In the existing art, to reduce detent torque and/or to adapt torque constant shape few methods are used, for in-stance lamination stack can be shifted/displaced versus each other. This method has a disadvantage in that it decreases torque constant of the motor.
[0005] According to another technique used in the existing art, shape of stator pole is selected such that the design thereof has low detent torque. As indicated above the objective of this technique is to keep the magnetic reluctance seen by the complete rotor to be constant. Electromagnetic simulation showed that by adapting shape of the pole we can have very low detent torque. With standard

lamination it is very difficult to achieve special pole shape especially with an axial
air gap and it's impossible to have a trapezoidal pole section in regard of magnet.
[0006] Thus, there is a need to provide a technique to reduce the detent torque
in axial flux disc magnet machines. The present disclosure has been devised to mitigate the above mentioned drawbacks.
[0007] It is an object of the present disclosure to reduce the detent torque and to have a sinusoidal torque constant profile without compromising on torque constant.
[0008] It is another object of the present disclosure to simplify the assembly process of the disc magnet motor using soft magnetic composite material. The powder metal core improves the performance of motor by optimizing the stator pole shape and section by decreasing the detent torque and achieving a sinusoidal torque constant.
SUMMARY OF THE INVENTION
[0009] The present disclosure addresses the problem of detent torque in axial flux disc magnet machines by optimizing shape and section of pole combined with the use of soft magnetic composite.
[00010] An aspect of the present disclosure relates to a stator assembly for an electric machine, the stator assembly including a plurality of poles formed of C-shaped laminated stacks of a soft magnetic composite material, each of the plurality of poles including at least two protruded portions having trapezoidal shape, each of the at least two protruded portions extending from a contact surface of the corresponding pole and tip surface of each of the at least two protruded portions facing each other to generate an opening accommodating magnetic poles of a rotor, wherein the at least two soft magnetic composite material based trapezoidal shaped protruded portions engender reduction in detent torque

generated by the electrical machine, thereby allowing generation of a constant
torque output.
[00011] In an embodiment, the rotor includes a magnet having substantially
annular disc shape.
[00012] In an embodiment, the plurality of poles are arranged substantially
perpendicular to a radial surface of the rotor.
[00013] In an embodiment, the at least two soft magnetic composite material
based trapezoidal shaped protruded portions reduce variability of magnetic
reluctance of the rotor.
[00014] In an embodiment, the stator assembly includes field windings coiled
around each of the plurality of poles.
[00015] In an embodiment, height of the tip surface of each of the protruded
portions is adapted such that the opening formed thereof produces an air gap
capable of reducing detent torque generated by the electrical machine.
BRIEF DESCRIPTION OF THE DRAWINGS
[00016] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present disclosure. Such accompanying drawings illustrate the structure, composition and purpose of the present disclosure to describe the principles of the present disclosure together with the description.
[00017] Fig. 1 illustrates a disc magnet motor according to an embodiment of the present disclosure.
[00018] Fig. 2 illustrates pole shape of the disc magnet motor according to an embodiment of the present disclosure.
[00019] Fig. 3a illustrates an exemplary representation of the disc magnet motor elemental magnetic circuit having "C" shape with lamination.
[00020] Fig. 3b illustrates an exemplary representation of the disc magnet type motor elemental magnetic circuit having "C" shape with soft magnetic composite

material having trapezoidal section and optimized pole shape according to an embodiment of the present disclosure.
[00021] Fig. 4 illustrates a graph of detent torque versus stator pole arc angle.
[00022] Fig. 5 illustrates a graph of Gamma (torque constant) versus stator pole arc angle.
[00023] The present disclosure discloses electrical machines, such as, axial flux disc magnet motor with reduced detent torque and sinusoidal torque constant profile. The present disclosure provides improved performance by optimization of stator pole shape and section by decreasing detent torque and achieving a sinusoidal torque constant.
[00024] According to an embodiment of the present disclosure, the soft magnetic composite (SMC) material based stator allows pole shaping to reduce the detent torque of the motor. The invention achieves the results by optimizing shape and section of stator pole combined with the use of soft magnetic composite material. The use of soft magnetic composite material is gaining interest due to three-dimensional flux capability, net-shaped single-piece components and low eddy current losses. Therefore, soft magnetic composite material based stator assembly simplifies manufacturing and improves motor efficiency while the torque constant is almost same.
[00025] Soft magnetic composites materials may be described as ferromagnetic powder particles surrounded by an electrical insulating film. SMC materials may be manufactured by compaction process combined with new techniques, such as two step compaction, warm compaction, multi-step and
magnetic annealing followed by a heat treatment at relatively low temperature.
[00026] In addition, the use of soft magnetic composite material allows the stator poles to have special shape capable of reducing the detent torque, and also to have lower magnetic flux density in the stator core due to bigger cross-sectional

area. This has a big advantage as It allow Increase in copper volume. Therefore, with this design we can optimize joules losses versus Iron losses for a given application.
[00027] As an example, we can drastically reduce the stator housing heat dissipation by 20% for textile machinery application having specific load profile.
[00028] Fig. 1 illustrates a disc magnet motor according to an embodiment of the present disclosure. The disc magnet motor 100 includes a stator assembly 102 including a plurality of poles 104 formed of laminated stacks of a soft magnetic composite material. The laminated stacks may be shaped in a manner so as to effectively guide magnetic flux to provide for generation of desired torque by the motor.
[00029] In an embodiment, the stator assembly 102 may include field windings coiled around each of the plurality of poles 104.
[00030] Each of the poles 104 may include at least two protruded portions having trapezoidal shape extending from a contact surface of the corresponding pole 104. A tip surface of each of the at least two protruded portions may face each other to generate an opening accommodating magnetic poles of a rotor 106 that may include a magnet having substantially annular disc shape. In an embodiment, the plurality of poles 104 may be arranged perpendicular to axial direction of the rotor 106. In another embodiment, the plurality of poles 104 may be arranged perpendicular to radial direction of the rotor 106.
[00031] The soft magnetic composite material based trapezoidal shaped protruded portions give rise to reduction in detent torque generated by the motor 100, and thus, enables generation of a constant torque output.
[00032] In an embodiment, height of the tip surface of each of the protruded portions is adapted such that the opening formed thereof produces an air gap capable of reducing detent torque generated by the motor 100.
[00033] It would be appreciated that although embodiments of the present
disclosure is explained in terms of a disc motor magnet, scope of the present

disclosure is not limited to the same in any manner whatsoever, and any other form of electrical machine that incorporates a stator assembly to aid generation of torque by utilizing magnetic forces is well within the scope of the present disclosure,
[00034] Fig. 2 illustrates pole shape of stator poles 202 of a stator assembly of a disc magnet motor according to an embodiment of the present disclosure. The shape of the stator pole 202 as shows in the figure helps in creating low detent torque in case of disc magnet motor.
[00035] In an aspect, the stator assembly may include a plurality of stator poles 202 formed of C-shaped laminated stacks of a soft magnetic composite material. Each of the plurality of poles 202 may include at least two protruded portions 204 having trapezoidal shape extending from a contact surface of the corresponding pole 202.
[00036] In an aspect, tip surface of each of the protruded portions 204 may face each other to generate an opening accommodating magnetic poles of a rotor 206, wherein the at least two soft magnetic composite material based trapezoidal shaped protruded portions 204 engender reduction in detent torque generated by the electrical machine, thereby allowing generation of a constant torque output.
[00037] In an embodiment, the rotor 206 includes a magnet having substantially annular disc shape.
[00038] In an embodiment, the plurality of poles 202 are arranged substantially perpendicular to a radial surface of the rotor 206.
[00039] In an embodiment, the soft magnetic composite material based trapezoidal shaped protruded portions 204 reduce variability of magnetic
reluctance of the rotor 206.
[00040] In an embodiment, the stator assembly Includes field windings coiled around each of the plurality of poles 202.

[00041] In an embodiment, height of the tip surface "X" of each of the protruded portions 204 is adapted such that the opening formed thereof produces an air gap capable of reducing detent torque generated by the disc magnet motor.
[00042] Fig. 3a illustrates an exemplary representation of the disc magnet motor elemental magnetic circuit 302 having "C" shape with lamination. Fig. 3b illustrates an exemplary representation of the disc magnet type motor elemental magnetic circuit 304 having "C" shape with soft magnetic composite material having trapezoidal section and optimized pole shape according to an embodiment of the present disclosure.
[00043] With typical C shape lamination 302 as shown in Fig. 3a, it is very difficult to achieve special pole shape especially with an axial air gap and it's impossible to have a trapezoidal pole section in regard of magnet to reduce the detent torque while soft magnetic composite material based stator allows the pole shaping with trapezoidal pole section to reduce the detent torque of the motor.
[00044] By virtue of soft magnetic composite material based trapezoidal shaped protruded portions 204 of the pole 202, detent torque generated by the disc magnet motor is reduced. Also, the trapezoidal geometry of the protruded portions 204 results in reduction in variability of magnetic reluctance of the rotor 206.
[00045] As illustrated in Figs. 2 and 3a, the protruded portions 204 of each of the poles 202 may extend from contact surface of the corresponding pole 202, and tip surface of each of the protruded portions 204 may face each other to generate the opening for accommodating magnetic poles of the rotor 206. The height of the tip surface of the protruded portions "X" may be adapted such that size of the opening Is reduced and air gap generated thereof reduces the detent torque generated by the disc magnet motor, thereby improving efficiency of the motor.
[00046] Fig. 4 illustrates a graph of detent torque versus stator pole arc angle.
It is to be noted that for a specific stator pole arc angle, when height of the tip surface "X" of the protruded portions 204 Is 0.3 mm, detent torque generated by
the motor is less than the detent torque produced by the motor when height of the

tip surface "X" of the protruded portions 204 is 0.2 mm. Hence, height of the tip surface of the trapezoidal shaped protruded portions 204 of the stator poles 202 is adapted such that the detent torque produced by the motor is reduced and the magnetic reluctance developed by the rotor 206 Is also compensated for.
[00047] Fig. 5 illustrates a graph of Gamma (torque constant) versus stator pole arc angle. It is to be noted that for a specific stator pole arc angle, when height of the tip surface "X" of the protruded portions 204 is 0.3 mm, gamma, i.e., torque constant generated by the motor is less than the detent torque produced by the motor when height of the tip surface "X" of the protruded portions 204 is 0.2 mm. Hence, height of the tip surface of the trapezoidal shaped protruded portions 204 of the stator poles 202 is adapted such that the gamma characteristics of the motor well within a prescribed range.
[00048] Further, it may be noted that for a higher degree of stator pole arc angle, the gamma characteristics reduces exponentially with an increase in height of the tip surface of the protruded portions 204 of the stator poles 202.
ADVANTAGES OF THE INVENTION
[00049] The proposed geometry of the stator poles reduces detent torque and assists the motor to have a sinusoidal torque constant profile without compromising on torque constant.
[00050] The proposed shape of the protruded portions of the stator poles reduces magnetic reluctance of the rotor and facilitates generation of a constant torque output.
[00051] The soft magnetic composite material based trapezoidal shaped protruded portions having extended tip surfaces tend to generate an air gap capable of aiding reduction in detent torque generated by the disc magnet motor.
DESC:AS ENCLOSED ,CLAIMS:CLAIMS
I/We Claim:
1. A stator assembly including:
a plurality of poles formed of C-shaped laminated stacks of a soft magnetic composite material, each of said plurality of poles including at least two protruded portions having trapezoidal shape, each of the at least two protruded portions extending from a contact surface of the corresponding pole and tip surface of each of the at least two protruded portions facing each other to generate an opening accommodating magnetic poles of a rotor of an electrical machine,
wherein the at least two soft magnetic composite material based trapezoidal shaped protruded portions reduce detent torque generated by the electrical machine, thereby allowing generation of a constant torque output.
2. The stator assembly of claim 1, wherein the rotor includes a magnet having substantially annular disc shape.
3. The stator assembly of claim 1, wherein the plurality of poles are arranged substantially perpendicular to a radial surface of the rotor.
4. The stator assembly of claim 1, wherein the at least two soft magnetic composite material based trapezoidal shaped protruded portions reduce variability of magnetic reluctance of the rotor.
5. The stator assembly of claim 1, wherein the stator assembly includes field windings coiled around each of the plurality of poles.
6. The stator assembly of claim 1, wherein height of the tip surface of each of the protruded portions is adapted such that the opening formed thereof produces an air gap capable of reducing detent torque generated by the electrical machine.
7. An electric machine including:
a rotor including a magnet having substantially annular disc shape; and
a stator assembly including a plurality of poles formed of C-shaped laminated stacks of a soft magnetic composite material, each of said plurality of poles including at least two protruded portions having trapezoidal shape, each of the at least two protruded portions extending from a contact surface of the corresponding pole and tip surface of each of the at least two protruded portions facing each other to generate an opening accommodating magnetic poles of the rotor,
wherein the at least two soft magnetic composite material based trapezoidal shaped protruded portions engender reduction in detent torque generated by the electrical machine, thereby allowing generation of a constant torque output.
8. The electric machine of claim 7, wherein the at least two soft magnetic composite material based trapezoidal shaped protruded portions reduce variability of magnetic reluctance of the rotor.
9. The electric machine of claim 7, wherein the stator assembly includes field windings coiled around each of the plurality of poles.
10. The electric machine of claim 7, wherein height of the tip surface of each of the protruded portions is adapted such that the opening formed thereof produces an air gap capable of reducing detent torque generated by the electrical machine.
Dated: 21.07.2017
(RITAM NARAYAN RAWAL)
IN/PA- 2055
REMFRY & SAGAR
ATTORNEY FOR THE APPLICANT [S]